1. Field of the Invention
The present invention relates to apparatus for measuring the mass properties of an object. More specifically, the invention relates to a gas-bearing suspension table and an electronics display/control unit for precisely determining rotational moments of inertia, center of gravity, and mass of items attached to the gas-bearing suspension table.
The apparatus of this invention employs monofilar torsional pendulum techniques for the determination of mass and distributed mass properties of a body. Using measured period data, the center of gravity location and principal axis moments of inertia can be accurately determined.
The basic method used in the mass properties measurement system of this invention to determine center of gravity and moment of inertia is the inverted torsional pendulum, where the test specimen is oscillated and the oscillation period measured. This principal has been widely used for many years; however, this invention is the first to recognize that the oscillation period measurements can be used to determine the center of mass coordinates and the mass of the specimen or test object.
2. Description of the Prior Art
Heretofore, inverted torsional pendulum measuring systems have included devices such as described in U.S. Pat. No. 3,693,413 issued Sept. 26, 1972 to R. S. Boynton and in Phillips, M. S., "Moment of Inertia System", Instruments and Control Systems, November 1966, pages 85-89. In apparatus of the Boynton type, the torsion wire provides the sole support for the test object mounting surface; the test object itself is mounted so that the rotational axis of the measurement system passes through the center of gravity of the test object. In such a system, the center of gravity of the test object must have been previously determined. Moreover, if the test object should be mounted such that its center of gravity is not coincident with the rotational axis of the system, the supporting torsion wire will be subject to severe lateral stress, resulting in measurement errors.
In the Phillips apparatus, the torsion rod is inserted into the specimen support table and aligned vertically after the test object has been aligned on the tables so that the axis about which the moment of inertia is to be determined is over the center of the table. The torsion rod is always inserted after the object is on the table and after the air pressure to the air bearing has been regulated to eliminate any compressive or tensile loads on the torsion rod. A principal disadvantage of test apparatus of the Phillips type is that it requires constant readjustment of the torsion rod each time a measurement on a different test object is to be made.
It is a feature and object of this invention to provide a gas-bearing mass properties measurement system which is simple to maintain and operate and with which the center of gravity and moments of inertia of a test object can be easily measured.
Other objects and features of this invention include:
1. A dual gas-bearing inverted torsional pendulum mass properties measuring apparatus.
2. A dual gas-bearing mass properties measurement apparatus capable of operating in terrestrial and extraterrestrial environments, including gravitationless environments found in manned spacecraft, such as orbiting space laboratories.
3. A mass-properties measurement apparatus in which a selected number of oscillation periods can be measured and averaged for each of several sets of angular coordinates to permit determination of the center of gravity and principal axis moment of inertia of a test object.
4. A dual gas-bearing mass-properties measurement system design which enhances stiffness and moment-carrying capability and in which moments applied as a result of off-axis loading have litte or no effect on the torsion wire.
5. A dual spherical gas-bearing mass properties measurement apparatus.